Blue moon: What is it and is it really blue?

You've heard the phrase "blue moon" thrown around, but what does it really mean?

It actually refers to the second full moon in a calendar month, which generally occurs once every few years.

Despite the name that suggests otherwise, a blue moon is rarely the color blue. In rare and unrelated circumstances, dust or smoke particles in the atmosphere can make the moon appear blue, according to AccuWeather.